Captain Scarlet and Captain Blue give chase to a mysteron replicant police officer, Rimmer, who has stolen a canister of deadly alien spores. The Mysterons plan to release the spores in the new Stellar City theme park in Phoenix. Rimmer loses the 2 agents and kills and Myseronises a motorcycle gang leader called Brock, who takes over from Rimmer. Scarlet and Blue are unware that Rimmer has passed the spores on to Brock and that they are looking for the worng person. Meanwhile Captain Ocher serches for a stolen Raid Bike, which was taken by a rival motorcycle gang leader named Colt who witnessed Rimmer kill Brock and is the only person who knows who now has the spores.